The present invention relates to a feed device.
Bipolar wet field diathermy in microsurgery is described in "Klinische Monatsblatter fur Augenheilkunde" (Clinical Ophthalmology Monthly), May, 1984, vol. 5, pp. 331-512. The possibility of hemostasis in the vitreous humor was investigated, starting with the first vitrectomies in 1972. A coaxial bipolar diathermy device was developed as a suitable instrument for the purpose. However, it is necessary to make sure that the heating is not too high for operations on the eye. The device was consequently equipped with an aspiration infusion irrigation device at that time to remove emerging liquid blood. It was possible to close the then visible hemorrhage source by coagulation.
It was then almost logical to replace the previous procedure for opening the capsule of the lens, namely that of cutting open the capsule sac, opening the capsule sac by perforation and then tearing, or by capsulorhexis, by a diathermy technique.
Two instruments were disclosed for the diathermic opening of the capsule sac.
In U.S. Pat. No. 4,367,744, an electrically insulating handpiece carries a cauterizing ring, which is fed with electric power to the handpiece from behind by one wire. In order for it to be possible for a current to flow, it was proposed to conduct the procedure with two wires to the cauterizing loop. On applying the cauterizing loop to the lenticular sac, the current produces heat in a range of from 500.degree. C. to 2000.degree. C. Such a high temperature may act for only a short time, and the cauterized site on the lenticular sac must be cooled as quickly as possible. Because the cauterizing loop must be introduced into the eye in already hot state in order to be able to perform the operation in as short a time as possible, it is necessary to proceed extremely carefully, in order not to injure any other parts of the eye.
U.S. Pat. No. 4,481,948 describes a cauterizing loop of similar type, but which is not heated with current flowing in the loop. A high-frequency 10 khz current is instead fed to the loop. An opposite pole is placed beneath the patient in order to close the circuit. The physician switches on the high-frequency circuit by means of a pedal.
High heat, which can be very injurious to the eye tissue, can also result with this arrangement. According to the older patent, the hot loop had to be introduced into the aqueous chamber until it could then be placed through the pupil into the posterior chamber onto the lenticular sac, in order to cauterize an opening there.
It is possible to activate, i.e., heat the loop with the high-frequency current as desired by the physician. The high-frequency current then can flow only when the loop is placed on a site covered with conducting liquid, thus on the lenticular sac. It is not possible to control the heat acting to produce coagulation at the border of the opening by this effect, so that mild injuries can result from the action of the heat.
Consequently, an object of the invention is that of controlling the current feed so that only precisely as much heat is produced for cutting the lenticular sac and coagulating the border of the hole, but protecting other tissues against heat action without additional feed.